Yasaman Zeinivand, Iraj Pakzad, Maryam Asadinezhad, Nazanin Omidi, Behrooz Sadeghi Kalani
Daptomycin effectively targets Listeria persisters, although efficacy varies by strain. The consistent clpP overexpression positions this protease as both a key persistence mediator and promising therapeutic target, potentially enhancing daptomycin-based interventions in food safety and clinical settings.
BACKGROUND: Listeria monocytogenes threatens food safety through biofilm formation and persistence of antibiotic-tolerant cells. This study investigates daptomycin's anti-persister effects and evaluates key molecular determinants to elucidate the underlying mechanisms.
METHODS: Five L. monocytogenes strains (serovars 1/2a-4e) were assessed using: (1) CLSI broth microdilution to determine daptomycin MICs, (2) gentamicin-induced persister killing assays followed by daptomycin treatment (1-2×MIC), (3) crystal violet quantification of daptomycin's biofilm inhibition/eradication at sub-MIC and therapeutic concentrations, and (4) qRT-PCR analysis of resistance/stress genes (mdrL, clpP, prfA, etc) during sub-MIC daptomycin exposure and in daptomycin-treated persisters.
RESULTS: Daptomycin showed strain-dependent activity (MICs: 2-8 μg/mL), completely eradicating most persisters at 2×MIC within 24 hours (residual 4e survival: 0.5 log10 CFU/mL). Biofilm inhibition varied from 58% (1/2a) to complete resistance (4e). Transcriptomics revealed clpP as the most upregulated gene (5-7-fold in persisters), with concurrent mdrL induction (4.8-fold) and prfA suppression. Membrane genes (mprF/dltA) showed moderate upregulation (1-5-fold).
CONCLUSION: Daptomycin effectively targets Listeria persisters, although efficacy varies by strain. The consistent clpP overexpression positions this protease as both a key persistence mediator and promising therapeutic target, potentially enhancing daptomycin-based interventions in food safety and clinical settings.